| In order to address the issues of energy shortage and environmental pollution,electric vehicles have received increasing attention and promotion from many countries.However,batteries generate a large amount of heat during operation,and high temperatures can cause aging and damage to batteries,thereby affecting the driving range and service life of electric vehicles,which undoubtedly limits the development of electric vehicles.To solve the battery heating problem,this article aims to design an energy-saving,efficient,and reliable cooling system.The article first analyzes the heat generation mechanism of batteries and the heat generation rate at different discharge rates,then analyzes the heat transfer mechanism of heat pipes and the heat transfer capacity of different concentration graphene oxide nanofluid heat pipes,and finally couples the battery with the heat pipe to build a vehicle-mounted power battery cooling system based on graphene oxide nanofluid heat pipes,and studies the heat dissipation performance of the system.Firstly,this paper introduces the basic structure and working principle of lithium manganate batteries,analyzes the reasons for heat generation during operation,and simulates the basic electrochemical characteristics of individual lithium batteries using numerical simulation methods,including charge discharge voltage characteristics,battery capacity attenuation,etc.Simulation calculations were conducted on the heat generation rate of individual batteries at different discharge rates(0.5C,1C,2C,3C,and 4C),and the curve of the heat generation rate of individual batteries over time was obtained,providing a data basis for subsequent analysis.In addition,the structure and working principle of gravity heat pipes were introduced.Fluent software was used to simulate the heat and mass transfer of gravity heat pipes,and the heat dissipation performance of different concentrations(0 wt%,0.025 wt%,0.05 wt%,0.1wt%)of graphene oxide nanofluid heat pipes was calculated through simulation.It was found that the evaporative and condensing heat transfer coefficients of the heat pipe increased with the increase of the evaporative section temperature,and when the concentration of graphene oxide was 0.1 wt%,the evaporative and condensing heat transfer coefficients of the heat pipe were the highest,and the heat transfer capacity was the best.The maximum evaporative heat transfer coefficient of 0.1 wt%nanofluid heat pipe was 1843.1 W/m~2·K,which was 38.7%higher than that of pure water heat pipe.The maximum condensing heat transfer coefficient was352.3 W/m~2·K,which was 34.7%higher than that of pure water heat pipe.The variation of the evaporative and condensing heat transfer coefficients of the heat pipe with the evaporative section temperature obtained from the simulation will serve as the heat dissipation boundary conditions for the vehicle battery cooling system.Finally,a vehicle power battery cooling system based on nanofluidic heat pipes was established and the cooling performance of the heat pipe cooling system of the battery under different discharge rates was studied.The study found that the maximum temperature and temperature difference of the battery pack using pure water heat pipes,0.025 wt%,0.05 wt%,and 0.1 wt%graphene oxide nanofluidic heat pipe cooling systems were reached at the end of discharge.When discharging at a rate of 1C,the maximum temperatures were 31.91℃,31.06℃,30.42℃,and 30.12℃,and the temperature differences were 1.22℃,1.25℃,1.28℃,and1.32℃,respectively.When discharging at a rate of 2C,the maximum temperatures were37.96℃,35.30℃,33.79℃,and 33.15℃,and the temperature differences were 2.02℃,2.21℃,2.35℃,and 2.52℃,respectively.When discharging at a rate of 3C,the maximum temperatures were 42.77℃,40.37℃,38.84℃,and 38.07℃,respectively.When discharging at a rate of 4C,the maximum temperatures were 61.68℃,52.40℃,48.90℃,and 47.46℃,and the temperature differences were 4.74℃,5.63℃,5.88℃,and 6.27℃,respectively.The study found that the highest temperature of the battery pack decreased with the increase of the concentration of graphene oxide nanofluid in the heat pipe cooling system,while the temperature difference of the battery pack increased with the increase of the nanofluid concentration,but the increase was not significant.When the battery was discharged at 3C rate,the heat dissipation performance of the nanofluid heat pipe cooling system was found to be significantly better than that of traditional air-cooled and water-cooled cooling systems.Both the heat pipe cooling system and water cooling system were able to maintain the temperature within a lower range,while the temperature of the air cooling system was higher.In terms of temperature consistency,the heat pipe cooling system performed the best. |
